. >>> and it could virtually paralyze the nation, defense secretary leon panetta is warning americans of a growing threat, a cyber attack by iran. >> a collective result of these kinds of attacks could be a cyber pearl harbor. >> defense officials tell nbc news that iran was behind a recent series of attempts to disable the websites to several major u.s. banks. now those attacks failed. but another iranian attack nearly shut down a saudi arabia oil company, experts say that type of attack should be a warning to the u.s. >> we don't have that type of security in the financial sector, the oil and gas sector, any of our critical infrastructures. >> leon panetta says that the industry must do more to combat those types of threats. >>> and tragedy on the tracks, we often hear about deadly accidents on our rails. in fact, there were two of them just last week. but how often is there trouble? we break down the numbers of accidents and deaths. >> reporter: we found that transit agencies spend millions every year to try to stop the tragedies. but the problem is not going away. in every one inv